Turning off cellphones or even locking them in metal boxes won’t be enough to keep them hidden with a new phone detector introduced on Monday.

The Manta Ray, made by Berkeley Varitronics Systems, can find phones through walls and other barriers even if their batteries and SIM cards are removed. The materials that the handheld detector can penetrate include aluminum, brass, copper, concrete and plasterboard, according to the company. The device, available from the company’s website for US$499, has been demonstrated in YouTube videos here and here.

The Manta Ray is designed for use in locations where phones are forbidden. A major market for such phone detectors is in prisons, where inmates often attempt to smuggle in handsets, but restricted sites also include sensitive government or corporate facilities that want to prevent unauthorized photography or electronic transfer of secrets, according to Scott Schober, president and CEO of Berkeley Varitronics. Instead of using invasive pat-downs or less-discriminating metal detectors, guards could do quick scans with the Manta Ray, which has a range of about six inches (15 centimeters), he said.

The Manta Ray could also have a role in espionage, detecting phones hidden in hotel rooms or even classic miniature “bugs,” though that’s not the company’s target market, Schober said. On a more pedestrian scale, it could be used in high schools where cell phones aren’t allowed. But movie theaters and concert halls, which some people wish could be free of cellphones, aren’t likely to put Manta Rays in the hands of ushers, according to Schober.

Metal detectors can’t distinguish between cellphones and other objects made with metal, and some phones have only small amounts of metal to be detected, Schober said. Conventional phone detectors, including ones Berkeley already sells, only work when phones are turned on because they depend on sensing the cellular signals coming out of the phone.

The Manta Ray uses neither of these techniques. Instead, it identifies specific components that are found in all cell phones, according to the company.

Schober wouldn’t name those components or say much else about how the Manta Ray works, other than that it uses an algorithm developed by Berkeley Varitronics to discriminate between phones and other items or substances nearby. It doesn’t transmit anything, doesn’t use x-ray or other optical methods and doesn’t detect chemical signatures in the air. Nor does it use UWB (ultrawideband), a technology that includes very low frequencies and has been used in ground-penetrating radar. It can be used anywhere in the world, Schober said.

Saying how the Manta Ray works would give away too much, Schober said, so his answers are tantalizingly vague.

“Is it operating within the realm of physical sciences and spectrum that we all know and accept? Yes,” Schober said. Beyond that, there’s not much. “We’re not focusing on what’s traditionally called radio frequencies,” he said.

If the Manta Ray is just a non-transmitting, passive sensor, there’s not much for it to sense, said Farpoint Group analyst Craig Mathias, a longtime student of many wireless technologies.

“A cellphone that is completely off emits no radiation that I’m aware of,” Mathias said. He suggested it might use magnetism.